Method and apparatus for manufacture of float glass

ABSTRACT

Float glass in manufactured with predetermined characteristics imparted to the glass by a body of molten material which clings to an electrode bar extending across the path of travel of a ribbon of float glass and which contacts the upper surface of the glass ribbon. The lower face of at least the downstream edge of the bar is formed of material sufficiently resistant to wear by the molten body to maintain constant the length of the body of molten material, in the direction of relative movement between the glass and the body, in any section through the body in that direction.

United States Patent Lawrenson et al.

1451 *Apr. 8, 1975 METHOD AND APPARATUS FOR MANUFACTURE OF FLOAT GLASSAssignee:

Pilkington Brothers Limited,

Liverpool, Lancashire. England Notice:

The portion of the term of this patent subsequent to Apr. 25, 1989. hasbeen disclaimed.

Filed:

Feb. 6, 1974 Appl. No.: 439.851

Related US. Application Data Continuation of Ser. No. 218.120. Jan. 17.1972. abandoned. which is a continuation-in-part of Ser. No. 810.248.March 25. 1969. Pat. No. 3.658.501.

Foreign Application Priority Data Apr. 9. 1968 United Kingdom 17077/68US. Cl 65/30; 65/99 A; 65/182 R;

204/196 Int. Cl. C03C 21/00 Field of Search... 65/99 A. 182 R. 101, 30;

[56] References Cited UNITED STATES PATENTS 3.108.939 10/1963 Sabins204/196 3.445.373 5/1969 Schuckeret a1. 204/225 X 3.515.659 6/1970 Proatet a1 204/224 M 3.607.175 9/1971 Robinson 65/99 A X 3.632.322 1/1972Loulges et a1. 65/99 A X 3.658.501 4/1972 Lawrenson et a1 65/182 R X3.684.680 8/1972 Heuze 204/196 Primary Examiner-S. Leon BashoreAssistant Examiner-Kenneth M. Schor Attorney. Agent. or FirmBurns,Doane. Swecker & Mathis [57] ABSTRACT Float glass in manufactured withpredetermined characteristics imparted to the glass by a body of moltenmaterial which clings to an electrode bar extending across the path oftravel of a ribbon of float glass and which contacts the upper surfaceof the glass ribbon. The lower face of at least the downstream edge ofthe bar is formed of material sufficiently resistant to wear by themolten body to maintain constant the length of the body of moltenmaterial. in the direction of relative movement between the glass andthe body. in any section through the body in that direction.

22 Claims, 9 Drawing Figures PATENTEDAPR 81975 SHIT 1 [IF 4 METHOD ANDAPPARATUS FOR MANUFACTURE OF FLOAT GLASS BACKGROUND or THE INVENTIONThis is a continuation of application Ser. .No. 218,120, filed Jan. 17,1972, and now abandoned.

Application Ser. No. 218120 is a continuation-inpart application ofcopending application, Ser. No. 810,248, filed Mar. 25, 1969 and nowPat. No. 3,658,501, and entitled Manufacture of Glass.

This invention relates to the manufacture of float glass, and moreespecially the invention concerns processes and apparatus for producingfloat glass in which predetermined characteristics are imparted to theglass by migration of an element or elements into the glass from a bodyof molten material which is held in contact with the surface of theglass.

In such processes the body of molten material .may be a molten metal ormolten alloy which clings to a locating member positioned adjacent teglass; surface. Relative movement is effected between the glass and thelocating member, and the molten body is maintained in position byclinging to the locating member. The migration of the element orelements into the glass from the body is controlled, for example, byregulating the oxidizing conditions at the interface between the glassand the body, as described and claimed in copending application, Ser.No. 765,428, filed Oct. 7, 1968 and now US. Pat. No. 3632322.Alternatively, an electrolytic method may be used, in which the locatingmember acts as an electrode and current is passed through the glass(which is electrically conductive at the elevated temperatures oftreatment) from the molten body to effect controlled migration of anelement or elements from the molten body into the glass.

As the process proceeds, material from the locating member is undercertain conditions dissolved by the molten body, resulting in anappearance of wear of the lower part of the locating member.

It is a main object of the present invention to maintain a desireduniformity of characteristic in the treated glass by maintainingconstant the intensity of treatment of each part of the glass throughouta manufacturing run of the process.

SUMMARY According to the invention there is provided a method ofproducing glass in which predetermined characteristics are imparted tothe glass from a body of molten material which contacts a surface of theglass and which clings to a locating member positioned adjacent saidglass surface, and in which relative movement is effected between theglass and the locating member, characterized by maintaining constant thelength of the body of molten material in the direction of relativemovement in any section through the body in that direction.

It has been found that parts of the locating member to which the moltenbody clings are more susceptible to wear than the rest of the locatingmember. Wear has been found at the front and rear faces of the lowerpart of the locating member. In a preferred embodiment of the inventionthis wear is obviated by providing that at least one edge portion of thelocating member, to which an edge of the molten body extendingtransversely of the direction of relative movement clings, is formed ofa material which is more resistant to wear by the material of the moltenbody than the remainder of the locating member. The wear resistantmaterial is preferablu located adjacent the downstream edge of thelocating member, i.e., the edge from which the treated glass emerges.

In apparatus according to the invention for effecting an electrolytictreatment of the glass, the locating member and the molten material areelectrically conductive and electrical connections are made to the 10-cating member and to the glass support means for passing electriccurrent through the molten body and the glass to assist the migration ofan element into the glass from the body of molten material.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a diagrammatic, partlycut-away, perspective view of an apparatus for treating glass in sheetform to which the present invention is applicable; and

FIGS. 2 to 9 are diagrammatic, cross-sectional views. each illustratinga different example of an insertreinforced locating member for use inapparatus according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Soda-Iime-silica glass, forexample, is fed on to the bath 3 at a controlled rate, either aspreformed ribbon of glass or as molten glass which is poured on to thebath at one end thereof and permitted to flow laterally unhindered tothe limit of its free flow under the influence of surface tension andgravitational forces to form a flat ribbon 4 of glass which is advancedalong the surface of the bath in the direction of arrow A.

The temperature of the glass ribbon 4 is regulated as theribbon isadvanced along the bath by means of controlled heaters (not shown)immersed in the bath 3 and located in the said headspace over the bath3.

A both 5 of molten material for modifying the upper surface of the glassis maintained in contact with the upper face of the ribbon 4, the body 5extending across the ribbon transversely of the direction of advance Athereof at a fixed station in the tank structure. The molten body 5,which does not wet the surface of the glass, is maintained in positionby an elongated locating member 6 extending transversely across theribbon 4 and parallel to the upper face thereof, so that a gap ofuniform depth (for example, about 3 to 4 mm) is maintained between thelower surface of the member 6 and the upper face of the ribbon 4.

The molten material of the body 5 wets the lower surface of 'thelocating member 6 and clings thereto, so that as the ribbon4 passescontinuously beneath the body 5, the latter is confined by the member 6to the gap between the member 6 and the ribbon 4.

The molten material of the body 5 may comprise a metal, an alloy or asalt. For example, the material may be tin, lead, bismuth, antimony,indium, zinc, or thallium. Examples of suitable molten alloys are alloysof tin or lead or bismuth as a solvent metal with lithium, sodium,potassium, zinc, magnesium, copper, or silver as a solute metal. Sodiumchloride is an example of a molten salt which may be used.

The locating member 6 may be of an unreactive metal, for example, one ofthe platinum group metals. Alternatively, the member 6 may comprise abase of, for example, copper, silver, brass, steel, alloys, containingcopper or silver, or a refractory material having a coating of anunreactive metal such as, for example. ruthenium.

As the glass ribbon 4 passes beneath the molten body, its surface ismodified by migration of.one or more elements from the body 5 into theglass surface.

In a preferred electrolytic process, the migration is controlled bypassing a regulated electric current through the body 5 and the ribbon 4to cause transfer of ions from the body 5 into the glass. For thispurpose. the locating member 6 is electrically conductive and isconnected to the positive terminal of a direct current supply source 7so that the molten body 5 acts as an anode and the bath 3 as a cathodeof an electrolytic circuit, the glass of the ribbon 4 being theelectrolyte. A negative electrode 8 connected to the negative terminalof the source 7 is immersed in the molten metal bath 3 on one side ofthe ribbon 4.

The surface modification of the glass ribbon 4 may alternatively beregulated by controlling oxidizing conditions in the body 5 so as toregulate the migration of an element or elements from the body 5 intothe glass.

A supply duct (not shown) is provided in the headspace adjacent themember 6 for replenishing the body 5 of molten material with the element(or elements) which migrates into the glass ribbon 4 in operation of theapparatus.

In order to ensure uniform surface treatment of the glass ribbon acrossits width, it is important to ensure that there is no variation in thesize of the gap between the lower surface of the locating member 6 andthe upper surface of the ribbon 4 along the width of the ribbon. Withthis object in view, the locating member 6 is supported from a rigidbeam structure 10 extending transversely over the bath 3.

The beam structure 10 is shown partially broken away in FIG. 1 for thesake of clarity. The beam struc ture 10 comprises two parallel,juxtaposed, boxsection, hollow beams 10a, 10b, through which a coolantfluid, conveniently water. is circulated so as to maintain the beamstructure 10 at a temperature which is considerably lower than thetemperature of the molten body 5 and locating member 6, whichtemperature is typically of the order of 700C.

The locating member 6 comprises an elongated strip having a flat lowerface, parallel to the surface of the ribbon 4 to which the molten body 5clings. Along its upper surface the member 6 is provided with anelongated key 11 which fits into a keyway 12 provided in an elongatedholder 13. In this way, the member 6 is free to undergo thermalexpansion relative to the holder 13 without restraint, and thereforewithout the occurrence of any deformation.

The holder 13 is suspended from the beam structure 10 by a plurality(four in the illustrated example) of support members 14, each of whichhas an enlarged T- shaped head which is located in longitudinallyextending slots 15 provided in the upper surface of the holder 13. Thespacing of the support members 14 along the holder 13 is so chosen thatthe natural bending of the holder and locating member 6 between adjacentsupport members 14 is less than an acceptable maximum. To compensate forthe tendency of the supported holder 13 and locating member 6 to flexunder gravity between the outer ends of the beam structure 10, at leastthe center ones of the support members 14 are made adjustable in length.For example, the support members 14 may comprise respective screw-jackdevices. A linkage is preferably provided for permitting adjustment ofthe support members 14 from positions externally of the tank structure.

By suitably adjusting the support members 14 and end supports (notshown) for the beam structure 10, the height of the gap between thelocating member 6 and the ribbon 4 can be maintained uniform withinacceptable limits over the length of the member 6.

It will be appreciated that the molten material in the body 5 is notstatic in operation of the apparatus, even though the body 5 as a wholeis held in the same position by clinging to the locating member. Sincethe lower face of the molten body 5 is in contact with the upper surfaceof the advancing glass ribbon 4, material in the body 5 close to theribbon 4 is carried along with the glass. A return flow in the oppositedirection takes place in the molten material close to the lower face ofthe locating member 6 resulting in some wear of the locating memberwhich in some instances is due to dissolving of the material of thelocating member 6 into the molten body 5, for example when the moltenbody 5 is a copper-lead alloy and the locating member 6 is a copper bar.Any such wear of the bottom of the locating member is usually uneven.

In the course of time, erosion of the trailing edge of the locatingmember 6 may locally increase the gap be tween the lower face of themember 6 and the upper face of the ribbon 4, to an extent such that themolten material can no longer remain in that part of the gap by surfacetension. As a result, the molten body 5 may recede unevenly from theeroded edge of the locating member 6.

The present invention avoids any such difficulty by ensuring that thelength of the molten body 5 in any section therethrough in the directionof glass advance is maintained substantially constant, so that themethod can be used with reliable results with high rates of glassmovement and with high currents.

At least the trailing edge portion of the locating member 6 isconstituted by a face of wear-resistant material to which the moltenmaterial of the body clings, and as shown in FIGS. 2 to 9, the locatingmember 6 is provided with an elongate insert 16 comprising a materialwhich is more resistant to erosion than the main body of the locatingmember 6. For example, where the locating member 6 is of copper and themolten body 5 is copper-lead alloy, the insert 16 may comprise iron,mild steel, ruthenium, nickel, or cobalt, each of which has a lowsolubility in the molten material of the body 5 which wets on to theinsert.

The insert 16 may be keyed into the locating member 6, as shown in FIGS.2, 3, and 5 to 9, or secured thereto by means of bolts, as in FIG. 4. Itis apparent that the lower face of the insert is fixed in relation tothe lower face of the upstream portions of the locating member. Toassist the initial wetting of the insert 16 by the molten body 5, theinsert 16 may be provided with a thin coating of copper, for example, byplating.

An insert 16 of porous refractory or porous graphite can conveniently beused when the molten body 5 is of molten lead or a lead alloy. Theporosity of graphite causes lead to be absorbed, giving a wettingeffect.

It has been found that the face of the locating member 6 may wear at itsleading edge 16a at a greater rate than over its main wetted surface,although the rate of wear is not as great as that which occurs at thetrailing edge. To avoid wear of the leading edge, it is also desirableto provide a further wear-resistant insert. similar to the insert 16shownin FIGS. 2 to 9. along the leading edge 16a of the wetted face ofthe locating member 6. The arrangement of FIG. 9 is particularlysuitable where the insert 16 is made. of porous graphite. a thin lip 17of the material of the locating member 6 (e.g.. copper) extendsinitially along the trailing edge face of the member 6. This lip 17after. a short period of operation is dissolved away to the limit shownin broken lines. This assists the initial wetting of the trailing edgeof the graphite insert 16. Thereafter, the trailing edge of the moltenbody 5 clings to the trailing edge of the insert 16, as shown in brokenlines.

Instead of an insert of wear-resistant material, the edges of thelocating member 6 may be plated so as to provide a wear-resistant face.For example, acopper bar may have its edges plated withruthenium.

The invention is described thereinabove with particular reference to thetreatment of glass in sheet or ribbon form, and'i's equally applicableto the treatment of glass articles, e. g., curved glass, pressed ware,or rolled glass sections.

The shape of the wetted surface of the locating member 6 andconsequently of the body 5 clinging thereto may be modified to suitparticular requirements. For example, the locating member 6 may have awidth in the direction of relative movement A of the glass which variesin a predetermined manner across the glass ribbon when it is desired toproduce a glass having shaded characteristicstransversely of the glass.

What is claimed is: 1. In a process of imparting surface characteristicsto a ribbon of float glass during manufacture thereof with improvedmaintenance of the intensity of treatment and uniformity of the impartedeharacteristics to a run of glass, the steps of:

advancing the ribbon of float glass along a molten metal bath providedin an elongated tank structure;

causing a molten metal body to wet onto and cling to the lower face of alocating member extending across the upper surface of said ribbon tolocate said molten metal body on the upper surface of said advancingribbon of glass such that relative movement occurs between said moltenmetal of said body and said lower face during glass advancement in amanner tending to wear a downstream edge portion of said lower face at agreater rate than upstream portions thereof;

enforcing migration of an element from said molten metal body into saidglass surface to impart surface characteristics to said glass ribbon;

providing said locating member in the form of a loeating member, thematerial of which is soluble in said molten metal body; and

stabilizing the location of the downstream edge portion of said moltenmetal body by providing a downstream edge portion of said lower face ofsaid locating member in the form of an edge portion of a material ontowhich said molten body wets and clings, which last-named material has agreater resistance to wear resulting from the moving molten metal ofsaid body than upstream portions of said lower face of said locatingmember, therby to improve maintenance of the intensity of treatment anduniformity of the imparted characteristics to a run of glass.

3. The method according to claim 1 including the step of causing thelower face of said downstream edge portion to be fixed in relation tothe lower face of said upstream portions. I

4. The method according to claim 1, wherein: said molten metal body isformed from a metal alloy; said locating member being formed of one ofthe constituent metals of the alloy, and

the downstream edge of the locating member being formed of a materialwhich has a low solubility the alloy. 5. The method according to claim4, wherein the molten metal body is a copper/lead alloy and the locatingmember is formed of copper.

6. The method according to claim 5, wherein said material having a lowsolubility in the alloy is iron.

7. The method according to claim 5, wherein said material having a lowsolubility in the alloy is ruthenium.

8. The method according to claim 5, wherein said material having a lowsolubility in the alloy is graphite. 9. The method according to claim 5,wherein said material having a low solubility in the alloy is nickel.

10. The method according to claim 5, wherein said material having a lowsolubility in the alloy is cobalt.

11. In a process of imparting surface characteristics to a ribbon offloat glass during manufacture thereof with improved maintenance of theintensity of treatment and uniformity of the imparted characteristics toa run of glass, the steps of:

advancing the ribbon of float glass along a molten metal bath providedin an elongated tank structure;

causing a molten body of glass-modifying material to cling to the lowerface of a locating member extending across the upper surface of saidribbon to locate said molten body on the upper surface of said advancingribbon of glass such that relative movement occurs between said moltenmaterial of said body and said lower face during glass advancement in amanner tending to wear a downstream edge portion of said lower face at agreater rate than upstream portions thereof;

enforcing migration of an element from said molten body into said glasssurface to impart surface characteristics to said glass ribbon; and

stabilizing the location of the downstream edge portion of said moltenbody by providing a downstream edge portion of said lower face of saidlocating member in the form of an edge portion of a material onto whichsaid molten body wets and clings, which last-named material. has agreater resistance to wear resulting from the moving molten metal ofsaid body than upstream portions of said lower face of said locatingmember, thereby to improve maintenance of the intensity of treatment anduniformity of the imparted characteristics to a run of glass.

12. Apparatus for imparting surface characteristics to a ribbon of floatglass during manufacture thereof with improved maintenance of theintensity of treatment and uniformity of the imparted characteristics toa run of glass, comprising:

an elongated tank structure containing a bath of molten metal;

means for advancing the ribbon of glass along the bath;

a locating member extending across said tank structure just above thesurface of said bath and having a lower face to locate a body of moltenglassmodifying material on the upper surface of said advancing ribbon ofglass such that relative movement occurs between said molten material ofsaid body and said lower face during glass advancement in a mannertending to wear a downstream edge portion of said lower face at agreater rate than upstream portions thereof; and

said lower face of said locating member including a downstream edgeportion formed from a material onto which said molten body wets andclings; said last-named material having a greater resistance to wearresulting from the moving molten material of said glass-modifying bodythan upstream portions of said lower face of said locating member,thereby to improve maintenance of the intensity of treatment anduniformity of the imparted characteristics to a run of glass.

13. Apparatus for imparting surface characteristics to a ribbon of floatglass during manufacture thereof with improved maintenance of theintensity of treatment and uniformity of the imparted characteristics toa run of glass, comprising:

an elongated tank structure containing a bath of molten metal;

means for advancing the ribbon of glass along the bath;

a locating member extending across said tank structure just above thesurface of said bath and having a lower face to locate a body of moltenglassmodifying metal on the upper surface of said advancing ribbon ofglass such that relative movement occurs between said molten metal ofsaid body and said lower face during glass advancement in a mannertending to'wear a downstream edge portion of said lower face at agreater rate than upstream portions thereof;

said lower face of said locating member being formed of a material whichis soluble in said molten metal body; and

said lower face of said locating member including a downstream edgeportion formed from a material onto which said molten body wets andclings; said lastnamed material having a greater resistance to wearresulting from the moving molten metal of said body than upstreamportions of said lower face of said locating member, thereby to improvemaintenance of the intensity of treatment and uniformity of the impartedcharacteristics to a run of glass.

14. Apparatus according to claim 13, wherein said downstream edgeportion comprises an elongate member which is attached to an upstreamportion of the 10- cating member.

15. Apparatus according to claim 14, wherein said elongate member iskeyed into an elongated channel formed in the locating member.

.16. Apparatus according to claim 14, wherein said elongate member isformed of iron.

17. Apparatus according to claim 14, wherein said elongate member isformed of mild steel.

18. Apparatus according to claim 14, wherein said elongate member isformed of ruthenium.

19. Apparatus according to claim 14, wherein said elongate member isformed of graphite.

relation to the lower face of said upstream portions.

1. IN A PROCESS OF IMPARTING SURFACE CHATACTERISTICS TO A RIBBON OFFLOAT GLASS DURING MANUFACTURE THEREOF WITH IMPROVED MAINTENANCE OF THEINTENSITY OF TREATMENT AND UNIFORMITY OF THE IMPARTED CHARACTERISTICS TOA RUN OF GLASS, THE STEPS OF: ADVANCING THE RIBBON OF FLOAT GLASS ALONGA MOLTEN METAL BATH PROVIDED IN AN ELONGATED TANK STRUCTURE; CAUSING AMOLTEN METAL BODY TO WET ONTO AND CLING TO THE LOWER FACE OF A LOCATINGMEMBER EXTENDING ACROSS THE UPPER SURFACE OF SAID RIBBON TO LOCATE SAIDMOLTEN METAL BODY ON THE SUPPER SURFACE OF SAID ADVANCING RIBBON OFGLASS SUCH THAT RELATIVE MOVEMENT OCCURS BETWEEN SAID MOLTEN METAL OFSAID BODY AND SAID LOWER FACE MURING GLASS ADVANCEMENT IN A MANNERTENDING TO WEAR A DOWNSTREAM EDGE PORTION OF SAID LOWER FACE AT AGREATER RAGE THAN UPSTREAM PORTIONS THEREOF, ENFORCING MIGRATION OF ANELEMENT FROM SAID MOLTEN METAL BODY INTO SAID GLASS SURFACE TO IMPARTSURFACE CHARCTERISTICS TO SAID GLASS RIBBON, PROVIDING SAID LOCATINGMEMBER IN THE FORM OF A LOCATING MEMBER THE MATERIAL OF WHICH IS SOLUBLEIN SAID MOLTEN METAL BODY, AND STABILIZING THE LOCATION OF THEDOWNSTREAM EDGE PORTION OF SAID MOLTEN METAL BODY OF PROVIDING ADOWNSTREAM EDGE PORTION OF SAID LOWER FACE OF SAID LOCATING MEMBER INTHE FORM OF AN EDGE PORTION OF A MATERIAL ONTO WHICH SAID MOLTEN BODYWETS AND CLINGS, WHICH LAST-NAMED MATERIAL HAS A GREATER RESISTANCE TOWEAR RESULTING FROM THE MOVING MOLTEN METAL OF SAID BODY THAN UPSTREAMPORTIONS OF SAID LOWER FACE OF SAID LOCATING MEMBER, THEREBY TO IMPROVEMAINTENANCE OF THE INTENSITY OF TREATMENT AND UNIFORMITY OF THE IMPARTEDCHARACTERISTICS TO A RUN OF GLASS.
 2. The method according to claim 1wherein said step of enforcing further comprises: electronicallyenforcing a migration of an element from said molten body into thesurface of the advancing glass ribbon.
 3. The method according to claim1 including the step of causing the lower face of said downstream edgeportion to be fixed in relation to the lower face of said upstreamportions.
 4. The method according to claim 1, wherein: said molten metalbody is formed from a metal alloy, said locating member being formed ofone of the constituent metals of the alloy, and the downstream edge ofthe locating member being formed of a material which has a lowsolubility in the alloy.
 5. The method according to claim 4, wherein themolten metal body is a copper/lead alloy and the locating member isformed of copper.
 6. The method according to claim 5, wherein saidmaterial having a low solubility in the alloy is iron.
 7. The methodaccording to claim 5, wherein said material having a low solubility inthe alloy is ruthenium.
 8. The method according to claim 5, wherein saidmaterial having a low solubility in the alloy is graphite.
 9. The methodaccording to claim 5, wherein said material having a low solubility inthe alloy is nickel.
 10. The method according to claim 5, wherein saidmaterial having a low solubility in the alloy is cobalt.
 11. In aprocess of imparting surface characteristics to a ribbon of float glassduring manufacture thereof with improved maintenance of the intensity oftreatment and uniformity of the imparted characteristics to a run ofglass, the steps of: advancing the ribbon of float glass along a moltenmetal bath provided in an elongated tank structure; causing a moltenbody of glass-modifying material to cling to the lower face of alocating member extending across the upper surface of said ribbon tolocate said molten body on the upper surface of said advancing ribbon ofglass such that relative movement occurs between said molten material ofsaid body and said lower face during glass advancement in a mannertending to wear a downstream edge portion of said lower face at agreater rate than upstream portions thereof; enforcing migration of anelement from said molten body into said glass surface to impart surfacecharacteristics to said glass ribbon; and stabilizing the location ofthe downstream edge portion of said molten body by providing adownstream edge portion of said lower face of said locating member inthe form of an edge portion of a material onto which said molten bodywets and clings, which last-named material has a greater resistance towear resulting from the moving molten metal of said body than upstreamportions of said lower face of said locating member, thereby to improvemaintenance of the intensity of treatment and uniformity of the impartedcharacteristics to a run of glass.
 12. Apparatus for imparting surfacecharacteristics to a ribbon of float glass during manufacture thereofwith improved maintenance of the intensity of treatment and uniformityof the imparted characteristics to a run of glass, comprising: anelongated tank structure containing a bath of molten metal; means foradvancing the ribbon of glass along the bath; a locating memberextending across said tank structure just above the surface of said bathand having a lower face to locate a body of molten glass-modifyingmaterial on the upper surface of said advancing ribbon of glass suchthat relative movement occurs between said molten material of said bodyand said lower face during glass advancement in a manner tending to weara downstream edge portion of said lower face at a greater rate thanupstream portions thereof; and said lower face of said locating memberincluding a downstream edge portion formed from a material onto whichsaid molten body wets and clings; said last-named material having agreater resistance to wear resulting from the moving molten material ofsaid glass-modifying body than upstream portions of said lower face ofsaid locating member, thereby to improve maintenance of the intensity oftreatment and uniformity of the imparted characteristics to a run ofglass.
 13. Apparatus for imparting surface characteristics to a ribbonof float glass during manufacture thereof with improved maintenance ofthe intensity of treatment and uniformity of the impartedcharacteristics to a run of glass, comprising: an elongated tankstructure containing a bath of molten metal; means for advancing theribbon of glass along the bath; a locating member extending across saidtank structure just above the surface of said bath and having a lowerface to locate a body of molten glass-modifying metal on the uppersurface of said advancing ribbon of glass such that relative movementoccurs between said molten metal of said body and said lower face duringglass advancement in a manner tending to wear a downstream edge portionof said lower face at a greater rate than upstream portions thereof;said lower face of said locating member being formed of a material whichis soluble in said molten metal body; and said lower face of saidlocating member including a downstream edge portion formed from amaterial onto which said molten body wets and clings; said lastnamedmaterial having a greater resistance to wear resulting from the movingmolten metal of said body than upstream portions of said lower face ofsaid locating member, thereby to improve maintenance of the intensity oftreatment and uniformity of the imparted characteristics to a run ofglass.
 14. Apparatus according to claim 13, wherein said downstream edgeportion comprises an elongate member which is attached to an upstreamportion of the locating member.
 15. Apparatus according to claim 14,wherein said elongate member is keyed into an elongated channel formedin the locating member.
 16. Apparatus according to claim 14, whereinsaid elongate member is formed of iron.
 17. Apparatus according to claim14, wherein said elongate member is formed of mild steel.
 18. Apparatusaccording to claim 14, wherein said elongate member is formed ofruthenium.
 19. Apparatus according to claim 14, wherein said elongatemember is formed of graphite.
 20. Apparatus according to claim 14,wherein said elongate member is formed of nickel.
 21. Apparatusaccording to claim 14, wherein said elongate member is formed of cobalt.22. Apparatus according to claim 14, wherein the lower face of saiddownstream edge portion is fixed in relation to the lower face of saidupstream portions.